To Plant or Not to Plant, that is the Question:
When deciding to put in a pond in the backyard, it can sometimes be difficult to decide between setting up a formal Koi pond, a natural fish pond or a water garden. Most first time pond keepers elect to set up a Koi pond since it is a simplier design, essentially a swimming pool for the Koi. It is only later that they get the itch to have some exotic pond plants and try to redesign the Koi pond. If the koi pond was designed with shallow areas along the sides of the pond, it will be possible to add marginal plants, though you may need to use planters that actually extend above the water level to keep the Koi from digging at the roots. You can also place medium size rocks on the top of the soil, though determined Koi can sometimes even move these out of the way to dig. Varieties of the Taro plant or Canna Lilies make some of the best marginal plants and add a spark of color to the pond. If the Koi pond did not have shallow areas, there is still an option if you have extra space around the pond. (This can also be used to modify a natural pond to add more plants.)
Making a Swamp in the Backyard:
This modification involves setting up a separate shallow pond and stocking it full of plants and allowing this pond to drain back into the original pond. The flow does not need to be very high. In fact it will work best if the flow rate per hour does not exceed the volume of the shallow pond. Depending on the terrain around the original pond, you can use either a short stream or waterfall to direct the water flow back to the Koi pond. The shallow pond will be stocked with enough plants to convert it to a natural filtration system, also called a bog filter. (This sounds more refined than calling it a swamp!) You will be using the plants to filter out excess nitrates and phosphates from the fish wastes and hopefully help control pond algae in the main pond. The bog pond will usually have a volume equal to about 1/10 or more of the main pond. You will to keep it rather swallow, maybe 1-2 feet deep. You could use one the prefab plastic ponds for the bog. You will want to almost fill the bog with dirt/potting soil to provide nutrients and soil for the roots. Alternatively you can place all the plants in individual planters to make it easier to remove or rearrange the plants. What type of plants you use to fill the bog will mostly be a matter of esthetics. The fast growing, dense plants like Varigated Sweetflag or Ribbon Grass can fill in an area and also act as a boarder/background for the rest of the bog pond. Different varieties of the popular Irises can add a splash of color to the bog. Another good accent plant is the Taro plant. It’s large leaves certainly stand out from the rest of the bog plants. If you are in a tropical area, you can also grow Dwarf Papyrus or Tropical Umbrella plant in dense clumps as boarder/background plants. If you do not have room next to the current pond for a new bog pond, you could section off an area of the pond and use planters to grow a dense clump of plants along one of the edges of the pond. You might have to use netting or plastic lattice to keep the Koi from this section. You will want to place a small water pump in the open section of the pond to pump water into the bog section, maybe with the use of an ornamental spitter.
Natural Algae Control:
The bog pond will act much like a small scale wetland to help purify the water. The growth of the plants will remove the nutrients responsible for the growth of nuisance algae, primarily the nitrates and the phosphates. Bog filters can remove other pollutants like heavy metals, pesticides and fertilizer that might be introduced to the pond from nearby lawn or garden treatments. Once established the area that is the bog filter will most likely not even look like a pond, just a section of attractive plant growth. As with almost all pond applications, be ready to make it bigger next year!